Fuel-cell-powered vehicles known today use hydrogen as their fuel; specifically, the fuel-cell-powered vehicles are provided with a traveling motor and a fuel cell stack that generates electric power using hydrogen and oxygen, so that they can travel by electricity. One example of a conventional fuel cell assembly is known from Japanese Patent Laid-Open Publication No. SHO-54-22537, and one example of a conventional fuel cell unit for use in an automotive vehicle is known from Japanese Patent Laid-Open Publication No. 2000-514745 (WO98/04013).
FIG. 13 hereof is a perspective view showing a fundamental construction of the conventional fuel cell assembly disclosed in the above-mentioned SHO-54-22537 publication. The disclosed conventional fuel cell assembly includes fuel cell laminates 201, and bipolar plates 202 arranged alternately with the fuel cell laminates 201 and each having fuel gas channels 203 and oxygen-containing gas channels 204. With such arrangements, the fuel cell laminates 201 can be cooled naturally with air.
The conventional fuel cell unit disclosed in the above-mentioned 2000-514745 publication includes a cooling system that cools fuel cells using traveling wind produced by traveling of an electric vehicle. The disclosed conventional fuel cell unit further includes a pressure source (e.g., air blower or fan) for compulsorily passing air through the cooling system, so that the fuel cells can be cooled by the fan during low-speed travel of the vehicle or when the ambient temperature is relatively high.
However, the conventional fuel cell assembly disclosed in the SHO-54-22537 publication is not satisfactory in that heat produced in the fuel cell laminates 201 can not be dissipated or removed easily. Namely, like other polymer-electrolyte-type fuel cell assemblies today, the disclosed fuel cell assembly is constructed to produce higher outputs, which would unavoidably lead to production of greater heat; in the conventionally-known fuel cell assemblies (fuel cell stacks), about 80% of the produced heat would remain in the assembly without being consumed by heat insulation, natural dissipation etc., and heat measures of the polymer-electrolyte-type fuel cells have therefore been one of the primary concerns. Although the air-cooled type fuel cell assemblies may have an advantage of simplified construction, they suffer from a poor cooling efficiency, so that, in the case where the polymer-electrolyte-type fuel cells, designed to produce higher outputs, are employed, there may arise a possibility of the temperature of the fuel cells getting excessively high, depending on the conditions. For these reasons, there has been a great demand for an improved fuel cell construction capable of effectively eliminating the produced heat.
The conventional fuel cell unit disclosed in the 2000-514745 publication is normally incorporated where a radiator of the vehicle is mounted, so that the cell unit (fuel cell stack) can be cooled directly by the traveling wind. In this case, however, there is a need for appropriately allocating air, introduced into an engine room of the vehicle, for two purposes, cooling and electric-power generating purposes, and a need for relating the flow rate of the air (oxygen) to an increase of the amount of the generated electric power and to the temperature of the fuel cell stack. Further, in the disclosed conventional fuel cell unit, where the air is introduced directly into the unit, air-side electrodes tend to be contaminated with foreign matters, such as dust and dirt, suspended in the air, which may thus result in a lowered electric power-generating performance.